The prior art has long recognized the versatility of perfluoroaromatic monomers in the production of polymers having high thermal stability. U.S. Pat. Nos. 3,694,495; 3,629,340 and 3,394,190 are exemplary of the use of such compounds as polymeric intermediates.
Further, such compounds have been employed as intermediates in the production of pyrethroid insecticides. For example, U.S. Pat. Nos. 4,385,070 and 4,486,355 disclose compounds of the formula ##STR3## wherein R is nitro, cyano, lower alkoxycarbonyl, lower alkylcarbonyl, or di- or trifluoromethyl which are used as intermediates in the production of benzyl esters having insecticidal and acaricidal activity. The compound wherein R is --CN may be prepared by carboxylation of the corresponding methyltetrafluorobenzene and subsequent derivativization of the carboxylic acid group, as set forth below: ##STR4## Since this reaction sequence and similar reaction sequences for producing such difunctional compounds are not particularly cost effective, alternative methods for the production of the difunctional intermediates are continuously being advanced.
A simplified method of producing para-substituted difunctional derivatives of pentafluorobenzonitrile would be by a Grignard synthesis.
However, the prior art teaches that the reaction of a Grignard reagent and a pentafluoroaromatic compound substituted with such electron withdrawing groups as --CN, --COR and --COOR, wherein R is an alkyl group, will not produce the desired para substituted compounds.
For example, Birchall et al in an early study illustrated that the reaction of pentafluorobenzonitrile (PFBN), represented by the formula ##STR5## with phenylmagnesium bromide in ether rendered pentafluorobenzophenone via the intermediate imine hydrochloride, C.sub.6 F.sub.5 CPh:N.sup.+ H.sub.2 Cl. (J. Chem. Soc. (C), 1971, 7, 1343).
Further, studies by T. N. Gerasimova show that when the starting reactants contain a --COOR group versus a -CN, the ortho substituted product is obtained, as represented by the following reaction mechanisms: ##STR6## where R =--CH.sub.3 or --CH(CH.sub.3).sub.2 ; and R.sup.1 =C.sub.1 --C.sub.4 alkyl or phenyl. Izv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk 1975, (5), 100-6.